Merge branch 'jt/config-lock-timeout' into seen

Configuration file locking now retries for a short period, avoiding
failures when multiple processes attempt to update the configuration
simultaneously.

* jt/config-lock-timeout:
  config: retry acquiring config.lock, configurable via core.configLockTimeout

diff --cc config.c
Simple merge

diff --cc t/t1300-config.sh
Simple merge